Bryophyte is a traditional name used to refer to all embryophytes (land plants) that do not have true vascular tissue and are therefore called "non-vascular plants". Some bryophytes do have specialized tissues for the transport of water; however, since these do not contain lignin, they are not considered to be true vascular tissue. , it is uncertain whether bryophytes are a natural or monophyletic group or a paraphyletic group, but the name is convenient and remains in use as a collective term for mosses, hornworts, and liverworts. Bryophytes produce enclosed reproductive structures (gametangia and sporangia), but they produce neither flowers nor seeds, reproducing via spores. The term "bryophyte" comes from Greek βρύον, bryon, "tree-moss, oyster-green" + φυτόν – phyton "plant".